The present invention relates to a projector apparatus for enlarging and projecting an image displayed on, for example, a transmission type liquid crystal display panel, onto a transmission type screen provided in the projector apparatus.
A projector apparatus of this type, for enlarging and projecting an image displayed on a cathode-ray tube (CRT), is known. However, such a projector apparatus requires the use of a high-luminance CRT, resulting in a very expensive and bulky apparatus.
The present invention proposes a projector using a liquid crystal display panel, inplace of a CRT.
This type of projector commands the displaying of an image on a transmission type liquid crystal display, then enlarges and projects the displayed image onto a screen. Projectors falling under this category include a type which projects an image onto a separate external screen and a type which projects an image onto a transmission type screen situated within the projector body.
FIG. 1 shows a conventional LCD-type projector for projecting an image onto a transmission type screen situated within the projector body. In FIG. 1, reference numeral 1 denotes the outer case of the projector. Display window 2 having transmission type screen 3 is located on the front surface of case 1. Reference numeral 4 denotes a transmission type liquid crystal display panel arranged to face screen 3 inside case 1. Reference numeral 5 denotes a light source for illuminating panel 4 from behind. Reference numeral 6 denotes a projection lens for enlarging and projecting a image displayed on panel 4 onto screen 3. Projection lens 6 is made up of a plurality of optical lenses. Light source 5 comprises high-luminance light source lamp 5a, and reflector 5b (a reflector having a parabolic reflection surface, for reflecting light from light source lamp 5a as parallel light) for reflecting illumination light from lamp 5a toward panel 4. An ultraviolet component is removed from the light emitted from light source 5 by ultraviolet absorption filter 7a and ultraviolet reflection filter 7b. The filtered light is then incident on panel 4, through condenser lens 8. Condenser lens 8 corrects the light incident on panel 4, so that it is aligned parallel to optical axis 0. When reflector 5b of light source 5 is a parabolic reflector, the light beams emitted from light source propagate toward panel 4, while at the same time being slightly diffused. Therefore, the light beams are corrected to be parallel beams by condenser lens 8, so that illumination light which is parallel to optical axis 0 can be incident on panel 4. Panel 4 comprises a dot-matrix display panel for displaying, for example, a television image. Optical image passing through panel 4, i.e., a display image on panel 4, is focused on projection lens 6 by circular Fresnel lens 9, and is enlarged and projected onto screen 3 of display window 2 by projection lens 6. FIG. 1 shows an LCD-type projector using a parabolic reflector as reflector 5b of light source 5. In a liquid crystal projector using an elliptic mirror surface reflector as the reflector, a relay lens is arranged between the light source and the liquid crystal display panel, so that light reflected by the reflector is corrected by the relay lens to be parallel light and is guided to the liquid crystal display panel.
In this liquid crystal projector, the display image on panel 4 is enlarged and projected onto screen 3 on the front surface of the projector body, and is watched from the front surface side of the projector body. With this projector, the display image on a small liquid crystal display panel can be enlarged and watched. In this liquid crystal projector, since screen 3 is provided to the projector body, the projection screen does not have a large size relative to a liquid crystal projector for projecting an image onto an external screen. However, since the external screen is not necessary, the above projector shown in FIG. 1 can be used in any location.
However, in the conventional liquid crystal projector shown in FIG. 1, projection lens 6, liquid crystal display panel 4, and light source 5 are linearly arranged with respect to transmission type screen 3. Therefore, the depth of case 1 is considerably increased, and hence, the projector becomes bulky as compared to the size of the screen projection surface.
Since an optical image projected onto screen 3 from its back surface side is watched from its front surface side, light from the internal optical system is partially reflected by the transmission type screen and cannot be often emitted outside the apparatus. For this reason, an optical loss is considerable, and a screen becomes dark.
The present invention has been made in consideration of the above situation and has as its object to provide a projector which can be rendered compact and can obtain a bright projection screen although it enlarges and projects a display image on a display apparatus onto a transmission type screen provided to a display window of a projector case.